OPTICAL ELEMENT DESIGNING METHOD, OPTICAL ELEMENT AND OPTICAL PICKUP DEVICE

摘要

Provided are a method for designing an optical element for an optical pickup device, an optical element and an optical pickup device. The optical element has excellent wavelength characteristics and suitably records and/or reproduces information on and/or from different optical discs but is easy to manufacture. A first basic structure and a second basic structure are superposed each other by having the directions of blazed portions of the structures opposite to each other, and while having a single optical path difference adding structure, which is easy to manufacture, the light quantity of a uth diffracted light of a first luminous flux is increased to the maximum and the light quantity of an xth diffracted light (x satisfies a formula (1)) is increased to the maximum. Thus, for instance, a spherical aberration due to the protection board thicknesses of a first optical disc and a second optical disc can be corrected, and a chromatic aberration due to changes of the light source wavelength of a first light source can be corrected (including elimination of chromatic aberration and giving a prescribed chromatic aberration), and the optical element for the optical pickup device is designed for suitably recording and/or reproducing information.